All I can guess is that is where you want to start, with the bolts just threading in at the bottom of the holes. As it torques down, the holes 'move down' and the bolts get higher in the holes (though you can't see it). If you started with the bolts in the middle or near the upper edges of the holes, then as it torqued down, the bolts might eventually bump into the upper edge of the holes, and then things would not completely settle down.